The relay device monitors if the physical switch is open or closed. You can sort of consider it the switch at one end of the hallway. The other end of the hallway is the digital switch that you can control on/off with a button, an interface, voice command, etc. The relay device then determines the combo of the two (is the black wire or the red wire powered from the far end of the hallway, and what is the physical position of the switch at the other end in a traditional 3 way setup?) and actually engages or disengages the actual relay/contact to the fireplace (R1).
- If relay is off, the digital switch is off, and the physical switch is "changed", then the relay is powered/closed/engaged and fireplace turns on.
- if the relay is already off, and the digital switch turns on, the relay powered/closed/engaged and fireplace turns on.
- if the relay is already on/powered/engaged, and the physical switch is "changed", the digital switch is turned off and the relay is unpowered/opened/disengaged and fireplace turns off.
- if the relay is already on/powered/engages, and the digital switch was on and is turned off, the relay is unpowered/opened/disengaged and fireplace turns off.
Slightly more complicated than a physical 3-way, but the effect is the same - control of the on/off of the fireplace using a combo of physical and/or digital switches.
